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    <h1>Introduction</h1>
    <p>
      Dragonfly Hall Reverb is a free stereo-to-stereo reverb effect.
      It is primarily intended for use as a concert hall reverb. It
      also has numerous smaller presets representing rooms, studios,
      and chambers.  It is based on Hibiki Reverb from Freeverb3VST,
      which uses Moorer's early reflection model and a modified FDN
      allpass Zita reverb.
    </p>
    <h1>User Interface</h1>
    <img src="images/dragonfly-hall-reverb/interface.png" />
    <h2>Sliders</h2>
    <img src="images/dragonfly-hall-reverb/sliders.png" />
    <dl>
      <dt>Dry Level</dt>
      <dd>
	<p>Level of the input signal sent directly to the reverb’s output</p>
      </dd>
      <dt>Early Level</dt>
      <dd>
	<p>Level of the early reflection signal in the reverb’s output</p>
      </dd>
      <dt>Early Send</dt>
      <dd>
	<p>Level of the early reflection signal mixed into the input to
	the late reverberation algorithm</p>
      </dd>
      <dt>Late Level</dt>
      <dd>
	<p>Level of the late reverberation signal in the reverb’s output</p>
      </dd>
    </dl>
    <p>
      The output of the Dry, Early, and Late controls are combined to
      form the reverb’s output signal. Note that sliders are not
      controlled by the presets. This allows you to set the levels in
      a way that works for your project, and then explore different
      presets without the sliders changing.
    </p>
    <h2>Basic Dials</h2>
    <p>
      Note that holding the Shift key and clicking a dial will reset
      the dial to the default for the current preset.
    </p>
    <img src="images/dragonfly-hall-reverb/size-width-dials.png" />
    <dl>
      <dt>Size</dt>
      <dd>
	<p>
	  Length of the reverb’s internal delay lines. Increasing the
	  Size parameter generally leads to a smoother, less resonant
	  output however it can also increase the reverb’s attack time
	  and make individual early reflections more
	  audible. Decreasing the Size parameter generally has the
	  opposite effect, decreasing the reverb’s attack time and
	  making individual early reflections less audible although it
	  can increase the presence of metallic resonances.
	</p>
	<p>
	  In physical terms, the Size control corresponds to the
	  largest dimension of an imaginary space. When the size is
	  small, the “walls” of this space are closer together and the
	  resultant reflection density increases. When the size is
	  large, that reflection density decreases. It is recommended
	  that for natural sounding reverbs the Size range be limited
	  to around 24 meters to 45 meters. However, there are many
	  useful reverbs that are outside this range.
	</p>
      </dd>
      <dt>Width</dt>
      <dd>
	<p>
	  The Width control sets the output stereo width. Note that
	  this applies to both the early reflections and the late
	  reverberation.
	</p>
      </dd>
    </dl>
    <img src="images/dragonfly-hall-reverb/predelay-decay-dials.png" />
    <dl>
      <dt>Predelay</dt>
      <dd>
	<p>
	  Delay before the onset of the late reverberation.
	</p>
	<p>
	  Note that only the late reverberation is delayed. Early
	  reflections are always output immediately. You can see this
	  by doing the following:
	  <ul>
	    <li>Set Early Level to 100% and Late Level to 0%.</li>
	    <li>Observe on the spectrogram that changing the Predelay does not move the early reflections.</li>
	    <li>Set Early Level to 0% and Late Level to 100%.</li>	    
	    <li>Observe on the spectrogram that changing the Predelay moves the late reverberation.</li>
	  </ul>
	</p>
      </dd>
      <dt>Decay</dt>
      <dd>
	Length of time for the late reverberation to decrease by 60dB.
      </dd>
    </dl>
    <h2>Preset Browser</h2>
    <img src="images/dragonfly-hall-reverb/presets.png" />
    <p>
      The Preset Browser section presents the user with a range of
      room, studio, and hall presets.
    </p>
    <h2>Spectrogram</h2>
    <img src="images/dragonfly-hall-reverb/spectrogram.png" />
    <p>
      The spectrogram has been included so that the user can get a
      better idea of how the various reverb parameters affect the
      plugin’s output. The spectrogram is rendered by simulating a
      burst of white noise through the reverb algorithm with the
      current settings, and then processing the output with a fast
      fourier transform algorithm.
    </p>
    <p>
      Clicking on the “?” displays the plugin name, version, license,
      and credits.
    </p>
    <h2>Advanced Dials</h2>
    <img src="images/dragonfly-hall-reverb/modulation-dials.png" />
    <dl>
      <dt>Diffuse</dt>
      <dd>
	<p>
	  Adjusts the coefficients of the allpass filters in the late
	  reverberation algorithm. It enables the user to balance echo
	  density against unpleasant colouration so that the result
	  enhances rather than detracts from the audio input signal.
	</p>
	<p>
	  A challenge that the designers of early digital reverbs
	  faced was generating a realistic number of early reflections
	  or echo density. One solution to this problem was to use
	  allpass filter networks. Although successful in increasing
	  echo density, the downside of allpass filter networks is
	  that they have a tendency to resonate, particularly when the
	  input signal is impulsive. This means that there is a
	  tradeoff between echo density and colouration.
	</p>
	<p>
	  In general, low echo density or diffusion settings increase
	  the perception of discrete echoes. In the case of
	  transient-rich sounds this can lead to “machine-gun-like”
	  effects in which individual echoes are heard. For sustained
	  sounds, this is less of an issue. Increasing the Diffuse
	  setting makes individual echoes less perceptible and
	  generally leads to a smoother, more lush reverb sound.
	  However it also can introduce metallic resonances which can
	  be noticeable but depend to a large extent on the nature of
	  the input signal.
	</p>
	<p>
	  To better understand the effects of the Diffuse control,
	  open a track with clear percussive sounds. Decreasing the
	  Diffuse value will result in fewer, more discrete
	  reflections in the late reverberation. When set at very low
	  values the late reverberation has an almost "shattering"
	  sound to it. A higher Diffuse setting results in the late
	  reverberation having a smoother and richer sound.
	</p>
      </dd>
      <dt>Modulation</dt>
      <dd>
	<p>
	  Level of modulation on the late reverberation signal. If
	  this is set to 0%, the following Spin and Wander dials will
	  have no effect.
	</p>
      </dd>
      <dt>Spin</dt>
      <dd>
	<p>
	  Rate of modulated chorus effect on the late
	  reverberation. In most cases, values from 1–2 Hz are
	  appropriate. Typically, these values should be smaller for
	  small rooms and chambers, however it’s always best to set
	  the parameters according to the musical context. Higher Spin
	  values can lead to an audible “wobble” particularly in real
	  instruments such as acoustic guitar or piano and can also
	  cause noise on pure tones. This effect tends to be less
	  noticeable on speech.
	</p>
      </dd>
      <dt>Wander</dt>
      <dd>
	<p>
	  Length of modulated chorus effect on the late reverberation,
	  measured in milliseconds.
	</p>
	<p>
	  To better understand the effects of Spin and Wander, set a
	  large room size, a long delay, Modulation to 100%, and
	  Wander to 0 ms. Then play an abrupt sound such as a
	  percussion hit or a chord on piano or guitar. You'll notice
	  the reverb tail panning alternately left and right in the
	  stereo field at the rate set by Spin control. There are
	  multiple layers to the late reverberation, but they are all
	  synchronised in the stereo space when Wander is set to 0
	  ms. Next, increase the Wander setting, which will make the
	  layers spread out in the stereo space. The layers all still
	  spin at the same rate, but at any given time each one has
	  its own location in the stereo field.
	</p>
      </dd>
    </dl>
    <img src="images/dragonfly-hall-reverb/high-dials.png" />
    <dl>
      <dt>High Cut</dt>
      <dd>
	<p>
	  Cutoff frequency of the reverb’s low pass filter, applied to
	  both the early reflections and late reverberation.
	</p>
      </dd>
      <dt>High Cross</dt>
      <dd>
	<p>
	  Short for High Crossover, the threshold in Hz above which
	  the High Multiplier parameter affects the high frequency
	  component of the late reverberation.
	</p>
      </dd>
      <dt>High Mult</dt>
      <dd>
	<p>
	  Short for High Multiplier. Multiplies the decay time of
	  frequencies above the High Crossover frequency. Applies only
	  to the late reverberation signal.
	</p>
      </dd>
    </dl>
    <img src="images/dragonfly-hall-reverb/low-dials.png" />
    <dl>
      <dt>Low Cut</dt>
      <dd>
	<p>
	  Cutoff frequency of the reverb’s high pass filter, is applied
	  to both the early reflectinos and late reverberation.
	</p>
      </dd>
      <dt>Low Cross</dt>
      <dd>
	<p>
	  Short for Low Crossover, the threshold below which the Low
	  Multiplier parameter affects the low frequency component of
	  the late reverberation.
	</p>
      </dd>
      <dt>Low Mult</dt>
      <dd>
	<p>
	  Short for Low Multiplier. Multiplies the decay time below
	  the Low Crossover frequency. Applies only to the late
	  reverberation signal.
	</p>
      </dd>
      <p>
	The Crossover and Multiplier parameters work together to
	determine the characteristics of the late reverberation. For
	example, with Decay set to 2.0s, High Crossover set to 5 kHz,
	and High Multiplier set to 0.8 X, frequencies above 5kHz will
	generally have a decay time of 2.0s x 0.8 = 1.6s. Note that
	the crossover frequency isn't a hard boundary, so the decay
	time will be ramped near the threshold. The same applies to
	the Low Crossover and Low Multiplier parameters. For example,
	with Decay set to 2.0s, Low Crossover set to 1 kHz and Low
	Multiplier set to 1.5, frequencies under 1 kHz will have a
	decay time of 2.0s x 1.5 = 3.0s.
      </p>

    </dl>
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